This invention relates to a novel composite material for the removal of noxious substances from a gaseous stream, and to the method for making the material. More particularly, this invention relates to a novel composite material which is effective in the removal of ozone from a gaseous stream.
In the electrophotographic reproducing arts, the usual practice is to deposit a uniform electrostatic charge on an imaging surface, with subsequent selective dissipation of the charge by exposure to a light image of an original document, to form an electrostatic latent image. The electrostatic latent image may then be developed and the developed image transferred to a support to form a copy of the original document. The deposition of the electrostatic charge is usually carried out by a corona device. In addition to precharging the imaging surface of an electrophotographic reproducing machine prior to exposure, corona devices are also commonly used to perform a variety of other functions in the electrophotographic reproducing process. For example, corona devices aid in the transfer of a toner image from a reusable photoreceptor to a transfer member, the tacking and the detacking of paper to the imaging member, and the conditioning of the imaging surface before and after the deposition of toner to improve the quality of the electrophotographic copies produced.
The operation of corona discharge devices, particularly at higher levels of output of corona charging, results in the formation of ozone in the atmosphere adjacent to the corona generator. As indicated in U.S. Pat. No. 3,983,393, increased copy speeds, as well as other requirements placed on modern copying and duplicating machines, have resulted in needs for higher outputs from the corona devices. This in turn has resulted in a need for an efficient ozone removing means. It is, of course, well known that ozone is extremely reactive and it can attack machine components as well as being toxic to humans. Relatively low concentrations of ozone in the atmosphere, for example from one part per thousand to one part per million, can cause headaches and nausea and irritation of mucus membranes.
Various ozone removing devices and methods have been proposed in the prior art. For example, in said U.S. Pat. No. 3,983,393, there is disclosed a corona device with reduced ozone emission. In the corona device of said patent, various configurations of ozone reducing members are interposed between the corona electrode and the corona shield to partially surround the corona electrode. Those ozone reducing members are coated with a catalytic material to reduce the ozone concentration. One such ozone decomposing material is a mixture of metallic oxides available as "hopcalite" from the Mine Safety Appliances Corporation.
In U.S. Pat. No. 3,675,096, there is disclosed a corona discharge device in which the corona generating electrode is enclosed within a housing having a foraminous screen as a portion thereof. A catalyst is disposed within the housing "to convert--ozone--to oxygen". Suitable catalysts disclosed in said patent include such metals as silver, gold, nickel, platinum, iron and their alloys. Also disclosed are certain metal oxides. Since the metal oxides do not lend themselves to being applied in the form of a catalytic coating, said U.S. Pat. No. 3,675,096 proposed that such oxides may be used by being disposed within the housing in foraminous screen containers.
In U.S. Pat. No. 4,110,425 there is disclosed a hydrogen-storing material which is made by mixing a hydrogen-absorbent material with a plastic material in emulsion or solution form, and then molding the mixture into desired shapes. The method of that patent for making shaped hydrogen-storing material is based on the there-stated finding that the hydrogen-absorbent material may be incorporated within the plastic material, with extensive coating of the surfaces of the hydrogen-absorbent material by the plastic material, without loosing hydrogen-storing capacity and without any reduction in the desorption rate.
U.S. Pat. No. 3,051,662 is another prior art patent disclosing a method for making catalyst structures in which the finely divided particles of the catalyst material is mixed with a polymer and the resulting mixture is compressed in a punch press to form the desired shape structures. Again, a substantial proportion of the catalyst particle is completely enclosed by the polymer matrix and thus does not come into direct contact with the outside atmosphere. Similarly, U.S. Pat. No. 3,775,192 discloses an analogous process for making catalyst tablets.
U.S. Pat. No. 3,926,851 discloses a method for preparing oxidation catalysts structures for use in automobile exhaust systems which is a porous ceramic base impregnated with suitable oxidizing agents. The method consists of shaping a ceramic filled polyolefin material containing a plasticizer, extracting the plasticizer, burning off the polyolefin, firing the porous shaped ceramic structure, and impregnating the structure, for example by slurry coating, with an engine exhaust oxidizing agent.
U.S. Pat. Nos. 3,381,454 and 3,925,248 disclose filter media for gases which is made of a plastic foam material and a catalytic material. In U.S. Pat. No. 3,381,454, the filter is made by incorporating the catalytic material in the polyurethane form material as the foam is being formed. In U.S. Pat. No. 3,925,248, the catalytic material is present in the form of small particles which are held in place by entrapment in the open pores and by surface Van de Waals forces in the foam plastic material.
Finally, U.S. Pat. Nos. 1,345,323 and 1,422,211 disclose hopcalite as a suitable catalyst for the treatment of gases.
Although hopcalite is a known catalyst for the decomposition of ozone, the foregoing prior art shows that it is difficult to use and there is a continuing need for improved methods and materials to take advantage of the catalytic activity of hopcalite. For example, if hopcalite is placed in the foraminous container of the device in U.S. Pat. No. 3,675,096, many problems would be created by such a usage. In the first place, hopcalite is a relatively expensive material, and the use of solid particles of hopcalite per se in a container will bring the result that only the surface of the hopcalite particles are utilized in the desired catalytic activity. Thus, with the use of relatively large hopcalite particles, most of the hopcalite is not effectively utilized. When fine particles of hopcalite particles are used in a bed, the pressure drop across an effective bed is relatively large, which may interfere with other machine functions in a copier/duplicator where sheets of paper are routinely and rapidly transported. Moreover, fine particles of hopcalite would be likely to escape the foraminous containers of U.S. Pat. No. 3,675,096 and cause contamination of macine components. If hopcalite particles are mixed with a plastic binder emulsion solution, see U.S. Pat. No. 4,110,425, the effectiveness of the hopcalite would be greatly diminished or completely negated. Accordingly, there is a need for improved method and materials for employing the catalytic activity of hopcalite to decompose ozone.